I have had good luck with uw-imap and dovecot. Dovecot seems to work better
in FreeBSD 5.21 though. I had problems with uw-imap crashing. Dovecot is
arguably more secure. The main drawback to dovecot is that it allows
multiple clients access to a mailbox at once. It works great for well
behaved clients but MacOS X's mail.app occasionaly screws up when deleting
and downloading new messages simultaneously with dovecot. It never occurred
with uw-imapd.
As for clients, I use mail.app on OSX, pine on the road through ssh (or when
booted into FreeBSD at home), and Outlook 2003. I had a lot of trouble with
Office XP's imap support, but it seems much better in 2003. Mozilla works
ok as well. Old versions of netscape mail didn't handle deleting messages
very cleanly.